[PATCH] eeprom: ee1004: add support for temperature sensor

[Heiner Kallweit <hkallweit1@gmail.com>]

The EE1004 SPD data structure advertises the presence of a thermal
sensor on a DDR4 module in byte 14, bit 7. Let's use this information
to explicitly instantiate the thermal sensor I2C client instead of
having to rely on class-based I2C probing.

The temp sensor i2c address can be derived from the SPD i2c address,
so we can directly instantiate the device and don't have to probe
for it. If the temp sensor has been instantiated already by other
means (e.g. class-based auto-detection), then the busy-check in 
i2c_new_client_device will detect this.

Patch was successfully tested with a Corsair Vengeance RGB PRO
DDR4 module which comes with a thermal sensor.

Link: https://www.spinics.net/lists/linux-i2c/msg65963.html
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
Patch is the same as the RFC version, it's just re-based.
---
 drivers/misc/eeprom/ee1004.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c
index fd12ce06a..21feebc30 100644
--- a/drivers/misc/eeprom/ee1004.c
+++ b/drivers/misc/eeprom/ee1004.c
@@ -182,6 +182,22 @@ static struct bin_attribute *ee1004_attrs[] = {
 
 BIN_ATTRIBUTE_GROUPS(ee1004);
 
+static void ee1004_probe_temp_sensor(struct i2c_client *client)
+{
+	struct i2c_board_info info = { .type = "jc42" };
+	u8 byte14;
+	int ret;
+
+	/* byte 14, bit 7 is set if temp sensor is present */
+	ret = ee1004_eeprom_read(client, &byte14, 14, 1);
+	if (ret != 1 || !(byte14 & BIT(7)))
+		return;
+
+	info.addr = 0x18 | (client->addr & 7);
+
+	i2c_new_client_device(client->adapter, &info);
+}
+
 static void ee1004_cleanup(int idx, struct ee1004_bus_data *bd)
 {
 	if (--bd->dev_count == 0) {
@@ -234,6 +250,9 @@ static int ee1004_probe(struct i2c_client *client)
 		dev_dbg(&client->dev, "Currently selected page: %d\n", err);
 		bd->current_page = err;
 	}
+
+	ee1004_probe_temp_sensor(client);
+
 	mutex_unlock(&ee1004_bus_lock);
 
 	dev_info(&client->dev,
-- 
2.43.0